Write#

Batch writing requires the compute engine to specify the target partition. For fixed-bucket tables, the engine must also assign a valid bucket to every RecordBatch. In unaware-bucket and postpone-bucket modes, the writer can resolve the bucket automatically when it is omitted.

Paimon C++ uses Apache Arrow as the in-memory columnar format to more efficiently support writing to disk columnar formats such as ORC, Parquet, and Avro, thereby improving write throughput.

Note

Currently supported table types:

  • Append table

  • Primary Key table

Not supported in the current scope:

  • Changelog

Bucketing Modes#

  • Append tables:

    • Support bucket = -1 (unaware-bucket mode)

    • Support bucket > 0 (fixed bucket mode)

  • PK tables:

    • Support bucket = -2 (postpone bucket mode)

    • Support bucket > 0 (fixed bucket mode)

Note

PK tables do not support dynamic bucketing (bucket = -1).

RecordBatch Construction#

  • The compute engine must:

    • Assign the correct partition for each row.

    • In fixed-bucket mode, apply the Paimon-consistent bucketing function, set a bucket in [0, bucket), and group rows into Arrow RecordBatch objects per partition-bucket combination.

  • In unaware-bucket mode (append table with bucket = -1), an omitted bucket is resolved to 0.

  • In postpone-bucket mode (primary-key table with bucket = -2), an omitted bucket is resolved to -2.

  • Recommended practices:

    • Use schema-aligned Arrow arrays with explicit validity bitmaps and offsets.

    • Prefer batch sizes tuned for I/O throughput (e.g., tens to hundreds of MB per flush, depending on filesystem and cluster configuration).

    • Maintain stable sort orders within a batch only if required by downstream merge or compaction logic; otherwise avoid unnecessary ordering costs.

Prepare Commit#

The compute engine is responsible for triggering the writer nodes’ PrepareCommit. Triggering conditions depend on the engine’s business needs and can follow either:

  • Streaming mode: time-based or periodic triggers (e.g., every N seconds).

  • Batch mode: trigger after all data in the batch has been written.

Once the compute engine collects CommitMessages from all writer nodes, it can issue a Commit request to the control plane (management path) to create a new Snapshot.

Compatibility Goals#

To ensure interoperability, the PrepareCommit result produced by Paimon C++ must be consumable by Paimon Java. Therefore:

  • The structure and semantics of CommitMessage must remain consistent with Java Paimon.

  • Any evolution of the Java-side CommitMessage schema must be tracked and validated on the C++ side to maintain cross-language compatibility.

Interface Design in Paimon C++#

Unlike Java Paimon, Paimon C++ does not expose BinaryRow-like types in its public interfaces. To preserve compatibility without leaking internal row representations, Paimon C++ provides CommitMessage only through:

  • Serialization: convert the internal commit state into a well-defined binary representation that matches Java Paimon’s expectations.

  • Deserialization: parse the Java-compatible binary representation back into C++ commit structures for validation, replay, or tooling needs.

This design ensures that:

  • Public APIs are independent of Java-specific row abstractions.

  • Cross-language commit payloads remain stable and versionable.

  • Internal data layouts can evolve without breaking external consumers.

CommitMessage Contract#

The CommitMessage must encode all information required by the coordinator to produce a correct Snapshot, which commonly includes (but is not limited to):

  • Partition and bucket identifiers associated with written data.

  • New data files, delete files (as applicable to the table type).

  • File-level metadata required for manifest and index updates (e.g., row counts, min/max statistics where applicable).

  • Transactional markers and sequence numbers as required by table semantics.

  • Any per-writer state necessary for deduplication or idempotent commits.

Note

The C++ writer supports Append and PK tables and can produce CommitMessage objects for both. FileStoreCommit supports direct file-system commits for both table types on non-object-store paths. Object-store paths require REST catalog commit mode. Changelog is out of scope and should not be emitted in CommitMessage until explicitly supported.

Serialization and Deserialization#

  • Binary format: The binary payload must strictly conform to Java Paimon’s CommitMessage encoding. It does not contain a version tag, so callers must transport CommitMessage::CurrentVersion() separately and supply it when deserializing.

  • Serialization API: Use CommitMessage::Serialize for one message or CommitMessage::SerializeList for a list.

  • Deserialization API: Use CommitMessage::Deserialize or CommitMessage::DeserializeList with the separately supplied serialization version.

  • Validation: Conformance and round-trip tests must verify compatibility with Java Paimon for supported message versions.

Operational Flow#

  1. Writer nodes perform data ingestion and produce Arrow RecordBatch organized by partition and bucket.

  2. Writers flush batches into ORC, Parquet, or Avro files via registered file.format and file-system backends, producing file-level metadata and per-batch commit state.

  3. Each writer invokes PrepareCommit, which: - Aggregates per-writer state into CommitMessage objects. - Returns CommitMessage objects; it does not serialize them.

  4. The compute engine gathers CommitMessage objects from all writers. For cross-process transport, it explicitly calls Serialize or SerializeList and carries CurrentVersion() alongside the payload.

  5. For a direct file-system commit on a non-object-store path, the engine passes the objects to FileStoreCommit for either an Append or PK table. For an object-store path, it enables REST catalog commit mode, calls Commit, obtains the JSON request from GetLastCommitTableRequest, and sends that request to the REST catalog.

  6. The local committer or REST catalog validates the messages, updates manifests/metadata, and finalizes the snapshot atomically.